There are many types of arthritis. The three most common are osteoarthritis, post traumatic arthritis and cuff tear arthropathy:
Primary osteoarthritis of the shoulder results from slow degenerative change in the shoulder joint and is related to the ageing process. Over time, cartilage on the joint surface becomes roughened and loses its lubrication properties. This can often result in stiffness and pain in the shoulder region.
Post-traumatic arthritis results from trauma to the shoulder region. This may involve a fracture or damage to the joint surface of the shoulder at the time of injury. Recurrent dislocations of the shoulder can also cause shoulder damage and destruction.
Cuff Tear Arthropathy (arthritis)
This is a combination of:
An ineffective and torn rotator cuff
Loss of central position of the shoulder joint with migration of the head of the humerus upwards
Degenerative changes in the shoulder joint, resulting from 1 and 2 above.
Not all people who have a rotator cuff tear will develop arthritis. It is only a certain portion of the population who have shoulders which are unable to function correctly after a tear in the rotator cuff who will develop this problem.